Yoshimura Mika, Oshima Taku, Ogasawara Naotake
Graduate School of Information Science, Nara Institute of Science and Technology, Ikoma, Nara, Japan.
BMC Microbiol. 2007 Jul 24;7:69. doi: 10.1186/1471-2180-7-69.
Phospholipid biosynthesis commences with the acylation of glycerol-3-phosphate (G3P) to form 1-acyl-G3P. This step is catalyzed by the PlsB protein in Escherichia coli. The gene encoding this protein has not been identified, however, in the majority of bacterial genome sequences, including that of Bacillus subtilis. Recently, a new two-step pathway catalyzed by PlsX and PlsY proteins for the initiation of phospholipid formation in Streptococcus pneumoniae has been reported.
In B. subtilis, 271 genes have been reported to be indispensable, when inactivated singly, for growth in LB medium. Among these, 11 genes encode proteins with unknown functions. As part of a genetic study to identify the functions of these genes, we show here that the B. subtilis ortholog of S. pneumoniae PlsY, YneS, is required for G3P acyltransferase activity, together with PlsX. The B. subtilis genome lacks plsB, and we show in vivo that the PlsX/Y pathway is indeed essential for the growth of bacteria lacking plsB. Interestingly, in addition to plsB, E. coli possesses plsX and the plsY ortholog, ygiH. We therefore explored the functional relationship between PlsB, PlsX and YgiH in E. coli, and found that plsB is essential for E. coli growth, indicating that PlsB plays an important role in 1-acyl-G3P synthesis in E. coli. We also found, however, that the simultaneous inactivation of plsX and ygiH was impossible, revealing important roles for PlsX and YgiH in E. coli growth.
Both plsX and yneS are essential for 1-acyl-G3P synthesis in B. subtilis, in agreement with recent reports on their biochemical functions. In E. coli, PlsB plays a principal role in 1-acyl-G3P synthesis and is also essential for bacterial growth. PlsX and YgiH also, however, play important roles in E. coli growth, possibly by regulating the intracellular concentration of acyl-ACP. These proteins are therefore important targets for development of new antibacterial agents.
磷脂生物合成始于甘油-3-磷酸（G3P）的酰化作用，形成1-酰基-G3P。这一步骤在大肠杆菌中由PlsB蛋白催化。然而，在包括枯草芽孢杆菌在内的大多数细菌基因组序列中，尚未鉴定出编码该蛋白的基因。最近，有报道称肺炎链球菌中由PlsX和PlsY蛋白催化的一种新的两步途径可启动磷脂形成。
在枯草芽孢杆菌中，据报道有271个基因在单独失活时对于在LB培养基中生长是不可或缺的。其中，11个基因编码功能未知的蛋白质。作为鉴定这些基因功能的遗传学研究的一部分，我们在此表明，肺炎链球菌PlsY的枯草芽孢杆菌直系同源物YneS与PlsX一起是G3P酰基转移酶活性所必需的。枯草芽孢杆菌基因组缺乏plsB，并且我们在体内表明PlsX/Y途径对于缺乏plsB的细菌生长确实至关重要。有趣的是，除了plsB外，大肠杆菌还拥有plsX和plsY的直系同源物ygiH。因此，我们探究了大肠杆菌中PlsB、PlsX和YgiH之间的功能关系，发现plsB对于大肠杆菌生长至关重要，这表明PlsB在大肠杆菌中1-酰基-G3P合成中起重要作用。然而，我们还发现，plsX和ygiH的同时失活是不可能的，这揭示了PlsX和YgiH在大肠杆菌生长中的重要作用。
与最近关于它们生化功能的报道一致，plsX和yneS对于枯草芽孢杆菌中1-酰基-G3P合成都是必不可少的。在大肠杆菌中，PlsB在1-酰基-G3P合成中起主要作用，并且对于细菌生长也是必不可少的。然而，PlsX和YgiH在大肠杆菌生长中也起重要作用，可能是通过调节酰基-ACP的细胞内浓度。因此，这些蛋白质是开发新型抗菌剂的重要靶点。
